This study was designed to determine if the surface modification of porous poly(lactic acid) (PLA) scaffolds would enhance osteogenic precursor cell (OPC) attachment, growth, and differentiation. A covalently grafted amino group (-NH(2)), poly(L-lysine) (PLL), and the peptide arginine-glycine-aspartic acid (RGD) were selected for the evaluation. The hypothesis was that surface modification would have a positive impact on cell-substratum interactions. The experiment was performed by OPC cells being placed on PLA films and scaffolds modified with NH(2), PLL, or RGD in tissue culture media. OPC attachment to PLA films was assessed after 24 h of incubation. The growth and differentiation of the adherent OPCs on porous PLA scaffolds were assessed after 14 and 28 days for alkaline phosphatase (APase) activity and calcium levels, both of which increase as OPCs differentiate into mature bone cells. All assays were accomplished in triplicate, and data were tested with post hoc orthogonal contrasts (i.e., Fisher's least significant difference) at p < or = 0.05. The PLA film surface-modified with RGD showed better OPC cell attachment than the other films. The cells on the PLA scaffolds surface-modified with RGD also exhibited an increase in APase activity and calcium levels in comparison with those on other scaffolds. This difference was apparent at both time intervals and was especially evident in the tissue culture media containing an osteogenic supplement. The results of this study indicate that modifying the surface of PLA polymer scaffolds with RGD enhances bone cell attachment and differentiation and may improve their ability to regenerate bone tissue more efficiently in wound models.

The present studies describe the fabrication and characterization of highly porous and interconnected poly(alpha-hydroxy acid) foam scaffolds produced using a phase separation multisolvent system, followed by a sublimation process. Fabrication parameters, including solvent composition, polymer concentration, freezing temperature, polymer type, and polymer molecular weight, were optimized to produce the desired foam microstructure. Analyses of selected samples with scanning electron microscopic images and mercury intrusion porosimetry indicated polymer foams with pore size ranges of 100-350 microm, a porosity >90%, and an interconnecting open-pore foam structure. Scaffold degradation profiles varied according to the type and molecular weight of the polymers. Cytocompatibility assays demonstrated that the preferred foam structures were nontoxic and osteoprecursor cells seeded into the scaffolds exhibited the ability to attach, propagate, and differentiate into a calcified structure.

Two new grafted polysiloxane polymers, a copolysiloxane and a terpolysiloxane, have been synthesized. Both polysiloxane backbones are grafted with dialkyl disulfide chains and 600 MW methoxy-terminated poly(ethylene glycol) (PEG) chains, while the terpolysiloxane also has 3400 MW PEG side chains terminated with N-hydroxysuccinimide (NHS) reactive ester groups. The two polymers spontaneously form monolayers on gold surfaces with estimated thicknesses of 23 and 31 Å, respectively. Combined analysis with angle-dependent X-ray photoelectron spectroscopy and static time-of-flight secondary ion mass spectrometry showed that most grafted dialkyl disulfide side chains were bound to the gold surface, forming multiple molecular linkages at the monolayer/gold interface. The PEG-grafted chains were concentrated in the outermost exposed region of the monolayers. Protein adsorption on the two immobilized polymer monolayers was examined with surface plasmon resonance (SPR). The copolymer-covered surface resisted protein adsorption from buffer, while the terpolymer monolayer bound significant amounts of protein. The NHS headgroup in the terpolymer was the primary site for protein binding. These two polymers have potential applications for SPR biosensor surface modification as protein-resistant and protein-immobilizing surfaces, respectively.

No abstract